Generally speaking, U.S. Pat. No. 3,155,046 to Vaughan, issued Nov. 3, 1964, discloses a centrifugal pump having a semi-open impeller with radial vanes. The vane edges adjacent to the pump inlet cooperate with sharpened leading edges of inlet apertures to cut stringy material or chunks entering the pump. Similarly, U.S. Pat. No. 3,973,866 to Vaughan, issued Aug. 10, 1976, and U.S. Pat. No. 4,842,479 to Dorsch, issued Jun. 27, 1989, disclose centrifugal pumps having impellers with vanes cooperating with inlet apertures to achieve a chopping or slicing action of solid material in a liquid or slurry being pumped. In the case of the pumps of U.S. Pat. No. 3,973,866 to Vaughan and U.S. Pat. No. 4,842,479 to Dorsch, however, semi-open impellers having shroud plates are used and external booster propellers may be provided to accelerate flow into the pump. The latter, when used, helps displace chunks of solid matter which become lodged in the inlet apertures and, at least in some instances cuts solid matter prior to entry into the pump.
One of the problems with each of these devices is the occurrence of motor overloading during heavy chopping. Where the chopping is not efficient, the motor power increases causing the motor protection controls to trip the motor offline. When the motor goes offline, the chopping stops and operator intervention is required to place the motor back online. The chopping down-time, of course, detracts from the cost effectiveness of the process.
Stringy material also presents a problem. The material becomes wrapped around the turning parts of the impeller assembly and can lead to plugging of the chopper pump inlet.
It is therefore desirable to provide an impeller assembly which helps maintain a clear cutting area, reduces cutting part wear and improves chopping efficiency to reduce motor power load and chopping down-time. It also would be desirable to provide an assembly which aggressively reduces the build-up and collection of stringy material, particularly around the external tool of the impeller assembly. The disclosed device affords other structural, manufacture and operating efficiencies not seen in prior art devices, as well.